Horizons and faults are fundamental geologic features that describe the geology, geometry and topology of the subsurface of the earth, which is imaged by the seismic method. Horizons are bounding surfaces of rock layers and are usually formed during depositional or erosional events. Horizons indicate generally vertical changes in rock material properties and bound rock volumes of economic interest. Faults compartmentalize the subsurface and are indicators of deformation over geologic time. Faults can act as permeable conduits or impermeable seals affecting the flow of subsurface fluids and gases and can also be drilling hazards. Hence, rapid and accurate mapping of geologic horizons and faults has high economic and safety value.
Roughly since Howard, in U.S. Pat. No. 5,056,066, introduced the idea of automatically tracking horizons in 3-D seismic data, a variety of methods for automatic and manual horizon extraction have been introduced. An article titled “Interactive seismic interpretation with piecewise global energy minimization” by T. Hollt, J. Beyer, F. Gschwantner, P. Muigg, H. Doleisch, G. Heinemann, M. Hadwiger in IEEE Pacific Visualization Symposium, pages 59-66, 2011 provides a recent survey. With few exceptions, horizon tracking has been posed as a local surface extension problem in which points exterior to a surface edge are individually evaluated for consistency with points on the surface edge and, if the exterior and edge points are similar enough by some measure, the exterior points are incorporated into the surface as new edge points. Thus the surface can grow from one or more user-selected seed points selected from examination of the seismic data, stopping when the exterior points are too dissimilar from the edge points to permit further growth or when the boundaries of the data are reached.
Quite often, the seismic image is sufficiently contaminated by noise that automatic horizon trackers either do not propagate the surface as far as is desirable (insufficient results) or, usually worse, propagate the surface in directions that do not correspond to actual geologic horizons (incorrect results). In the first case, the analyst typically inserts additional seed points or lowers the similarity threshold to promote surface propagation. In the second case, the analyst may either raise the similarity threshold or manually edit the surface to remove undesirable portions of the extracted surface. The combination of a difficult-to-control automatic extraction process with subsequent manual editing and further automatic extraction can lead to results that are highly dependent on the sequence of tedious analyst actions and are thus generally irreproducible.
For typical noisy seismic images, a mixture of manual and automated interpretation is required. This invention is a semi-automated computer-based process that reduces the time consuming nature of horizon interpretation, while simultaneously increasing the fidelity and reproducibility of the extracted horizon surfaces and at the same time allowing an analyst to manually interpret and modify the automatically extracted surfaces in regions of poor image quality.
It is desirable to provide a process that significantly reduces the time required for interpretation, while increasing the accuracy and reproducibility of the extracted horizon surfaces and it is to this end that the disclosure is directed.